1. Field of the Invention
A liquid level and temperature sensing device fOr monitoring and measuring the level of liquid and temperature stored within a tank or reservoir.
2. Description of the Prior Art
U.S. Pat. No. 4,726,226 shows a device to measure the volume of the contents of a tank and the temperature or other parameter to be reported to a central data collection area for recording and control.
U.S. Pat. No. 4,305,283 describes an apparatus for indicating the level of liquid in a tank including a float resting on the surface of the liquid connected by a wire or chain to a level sensing mechanism so that movements of the float due to changes in the liquid level, are communicated to the mechanism. The mechanism may register and/or indicate the height of the level and produce electrical signals corresponding to the height of the level.
The use of electrical sensing devices such as floating controlled variable resistors can reduce the friction problems associated with such devices. In addition, if the liquid is flammable precautions should be taken to prevent ignition of the liquid by electrical sparks. A common method to overcome these problems is to extend a mechanical linkage through the wall of the tank and connect the linkage to electrical sensing and indicating equipment outside the tank. However, such linkages are also prone to friction problems.
U.S. Pat. No. 3,898,555 relates to a sensing device employing a Wiedemann Effect.
U.S. Pat. No. 4,726,226 describes sensing the temperature of liquid in a tank accomplished by the use of either temperature sensitive resistors or of temperature sensitive semiconductor devices. Such sensors typically provide a voltage indicative of the temperature of the region in which such devices are located. For most tank situations, for example, there will be a desire to know the temperature at several locations in the tank and therefore, several sensors are located about the tank at those locations.
The results measured concerning the liquid contents of a tank in this example must then be conveyed to the user.
U.S. 4,305,283 shows a position determining apparatus comprising a taut electrically-conductive member; a pulse generator to feed a pulse of electric current along the member; a magnet located at a variable first point along the member, for example on a float on the surface of a liquid the level of which is to be determined, to apply a magnetic field to the member at that point; and a transducer positioned at a second point along the member to sense the arrival at the second point of a mechanical impulse induced in the member by interaction between the current pulse and the magnetic field as the current pulse passes the magnet. A time measuring circuit responsive to the time interval between the feeding of the current pulse and the arrival of the mechanical impulse at the second point is used to determine the position of the first point.
U.S. Pat. No. 4,726,226 describes a measurement system for remotely measuring a parameter and relative distance having a parameter sensor providing signals to control the pulse repetition rate of a pulse generator, the pulses from the pulse generator in turn controlling a switch to alternately connect and disconnect an energy storage device to the input of a sonic waveguide device. The output signals at the outputs of the sonic waveguide device control a driving device which provides a representation of these output signals on a transmission line arrangement.
U.S. Pat. No. 3,898,555 relates to a linear distance measuring device to measure the time it takes a torsion pulse to traverse a sonic waveguide from a movable magnet to a pulse responsive element is determined and converted to a measurement of the distance from the movable magnet to the pulse responsive element. The position of the magnet moved by an external means such as a machine tool element can thus be determined precisely.
U.S. Pat. No. 4,361,037 describes a device for electric monitoring of the level of a liquid present in a tank, with a temperature-dependent resistance probe which is immersed in the liquid the level, a source of constant current connectable, controlled by a timer, to the resistance probe, a circuit, controlled by the timer, for detecting and storing an initial voltage drop on the resistance probe at an initial time and a measurement voltage at a defined time after the connection of the source of constant current, and a circuit for evaluating these voltages by subtraction of the measurement voltage from the initial voltage and if necessary under circumstances inversion of the difference in order to form a display voltage which corresponds to the level. There are provided a resistance probe structure for compensating for the influence of the change in level of the liquid on the display voltage due to thermal expansion as a function of its initial temperature and a computation circuit for compensating for different heat transfers from the resistance probe to the liquid as a function of the initial temperature.
U.S. Pat. No. 4,571,095 relates to a device for measuring a temperature comprising a first resistance, the resistance valve of which depends on the temperature to be measured, a second resistance, a multiple switch with a plurality of inputs and an output, wherein the resistances each are connected to a corresponding input, a supply source which can be coupled with both resistances through a switch and a processing unit for controlling the switch and the multiple switch and for determining the temperature in dependence on the voltages measured at the supply source being switched on and off respectively, in the subsequent positions of the multiple switch. The output of the multiple switch is connected to an input of voltage/frequency converter through a voltage source, an output of the voltage/frequency converter being connected to the processing unit.